Effect of Bacterial Biofilm on the Osteogenic Differentiation of Stem Cells of Apical Papilla.

Introduction: Although clinical success in regenerative endodontics is substantially high, histological success is limited to finding bone/cementum-like tissue instead of dentin within the canal space. The aims of this study were to investigate (1) the effect of bacterial biofilm on osteogenic gene expression in stem cells of the apical papilla (SCAP) and (2) the effect of bacterial antigens on the functional differentiation of SCAP into a mineralizing phenotype.

Methods: Using an ex vivo organotypic root canal model and an American Association of Endontists-recommended regenerative endodontic procedures, we evaluated SCAP differentiation in the presence and absence of an Enterococcus faecalis biofilm. Gene expression analysis for dentinogenic and osteoblastic markers was performed with real-time polymerase chain reaction. The effect of E. faecalis antigens on SCAP differentiation into mineralizing cells in vitro was evaluated with 2 functional assays: Alizarin Red and alkaline phosphatase activity assays.

Results: After regenerative endodontic procedures, residual bacteria continued to sustain within the root canal system. SCAP in the presence of E. faecalis biofilm significantly downregulated dentinogenic genes such as dentin sialophosphoprotein and upregulated osteoblastic genes such as bone sialoprotein, osteocalcin, distal-less homeobox 5, and runt-related transcription factor 2. E. faecalis antigens significantly inhibited SCAP differentiation into a mineralizing phenotype when alizarin red staining and alkaline phosphatase assays were used in vitro.

Conclusions: Current disinfection protocols were ineffective in eliminating bacteria from root tips and the levels of the residual bacterial biofilm, and its byproducts, were able to significantly alter osteogenic-differentiation of SCAP.